PHYS 4580, PHYS 6/7280The University of Toledo

Profs. R. Ellingson and M. Heben

Absorption coefficients of semiconductor thin films

November 1, 2011

Quiz #1 results

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Freq

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1086420Score

Quiz 1

Sheet Resistance (revisited)

http://en.wikipedia.org/wiki/Sheet_resistance

Regular 3-D conductor, resistance R is:WtL

ALR ρρ ==

where ρ is the resistivity (Ω⋅m), A is the cross-section area, and L is the length. For A in terms of W and t,

WLR

WL

tR s== ρ where Rs is the Sheet Resistance. Units are ohms,

but can also express this as “ohms per square, or Ω/⃞, or Ω/sq.

• A square sheet with an Rs of 100 Ω/⃞ has a resistance of 100 Ω (regardless of the size of the square).

Sheet Resistance – importance of film morphology

Scanning Electron Microscope (SEM) image of ~15 nm thick Au deposited by thermal evaporation.

Sheet Resistance – importance of film morphology

Scanning Electron Microscope (SEM) image of ~2.7 nm thick Cr deposited by sputtering from a Cr target.

Sheet Resistance – importance of film morphology

Scanning Electron Microscope (SEM) image of ~15 nm thick Cr deposited by sputtering from a Cr target.

Sheet Resistance – importance of film morphology

Thin metal films

“The sheet resistance values corresponding to the 2, 3.1, 4.5 and 8 nm are 5x103, 1.6x103, 4x102 and 1x102 Ω/⃞, respectively.”

For a Single Absorber Device

Indirect and Direct Band Gaps

From Wikipedia

Goals of the Absorption Coefficient Determination Lab (Unit) –address these in your lab report:

1) Measure the optical absorption coefficient for CdS and CdTe films provided.

2) Determine type and size of the band gap for CdS and CdTe

3) Measure the absorption spectrum of the TCO/CdS/CdTe film stack and estimate the thickness of the CdTe and CdS layers in the stack using the data obtained in (1).